Large numerical aperture bend resistant multimode optical fiber

ABSTRACT

Bend resistant optical fibers which are multi-moded at 1300 nm include a core, an inner cladding, a low index ring and an outer cladding. The core has a graded index of refraction with a core alpha profile where 1.9≦α C ≦2.1, a maximum relative refractive index percent Δ 1Max %, and a numerical aperture NA of greater than 0.23. The inner cladding surrounds the core and has a maximum relative refractive index percent Δ 2Max %, a minimum relative refractive index percent Δ 2Min %, and a radial thickness ≧0.5 microns, wherein Δ 1Max %&gt;Δ 2Max %. The low index ring surrounds the inner cladding and has a relative refractive index percent Δ 3 %, a radial thickness of at least 0.5 microns, a profile volume with an absolute magnitude of greater than 50%-μm 2 , wherein Δ 2Min %≧Δ 3 %. The outer cladding surrounds the low index ring and has a relative refractive index percent Δ 4 %, such that Δ 1Max %&gt;Δ 4 %≧Δ 2Max %.

BACKGROUND

1. Field

The present specification generally relates to optical fibers and, morespecifically, to multimode optical fibers having large numericalapertures and improved bend performance.

2. Technical Background

Corning Incorporated manufactures and sells InfiniCor® 62.5 μm opticalfiber, which is multimode optical fiber having a core with a maximumrelative refractive index delta of about 2% and 62.5 μm core diameter,as well as InfiniCor® 50 μm optical fiber, which is multimode opticalfiber having a core with a maximum relative refractive index delta ofabout 1% and 50 μm core diameter. It would be desirable to developalternative multimode fiber designs, particularly optical fiber designswith high numerical apertures that would enable improved bendperformance and higher bandwidth.

SUMMARY

According to one embodiment, a bend resistant optical fiber which ismulti-moded at 1300 nm includes a core, an inner cladding, a low indexring and an outer cladding. The core may be formed from silica-basedglass and has a graded index of refraction with a core alpha profilewhere 1.9≦α_(C)≦2.1, a maximum relative refractive index percentΔ_(1Max)% relative to the outer cladding, and a numerical aperture NA ofgreater than 0.23. The inner cladding surrounds and is in direct contactwith the core, the inner cladding having a maximum relative refractiveindex percent Δ_(2Max)% relative to the outer cladding, a minimumrelative refractive index percent Δ_(2min)% relative to the outercladding, and a radial thickness of at least 0.5 microns. Δ_(1Max)% ofthe core may be greater than Δ_(2Max)% of the inner cladding. The lowindex ring may surround and be in direct contact with the inner claddingsuch that the low index ring is spaced apart from the core. The lowindex ring has a relative refractive index percent Δ₃% relative to theouter cladding, a radial thickness of at least 0.5 microns and a profilevolume with an absolute magnitude of greater than 50%-μm². The minimumrelative refractive index percent Δ_(2Min)% of the inner cladding isgreater than or equal to Δ₃% of the low index ring. The outer claddingsurrounds and is in direct contact with the low index ring and may havea relative refractive index percent Δ₄% relative to pure silica glasssuch that Δ_(1Max)%>Δ₄%≧Δ_(2Max)%.

In another embodiment, a bend-resistant optical fiber which ismulti-moded at 1300 nm includes a core, an inner cladding, a low indexring, and an outer cladding. The core may be formed from silica-basedglass and comprises a graded index of refraction with a core alphaprofile where 1.9≦α_(C)≦2.1, a maximum relative refractive index percentΔ_(1Max)% relative to the outer cladding, and a numerical aperture NA ofgreater than 0.23. The inner cladding may surround and be in directcontact with the core and have a graded index of refraction with aninner cladding alpha profile α_(IC), a maximum relative refractive indexpercent Δ_(2Max)% relative to the outer cladding, and a minimum relativerefractive index percent Δ_(2Min)% relative to the outer cladding,wherein Δ_(1Max)%>Δ_(2Max)%. The low index ring may surround and be indirect contact with the graded index inner cladding such that the lowindex ring is spaced apart from the core, the low index ring having arelative refractive index percent Δ₃% relative to the outer cladding, aradial thickness of at least 1 micron and a profile volume with anabsolute magnitude of greater than 50%-μm², wherein Δ_(2Min)%≧Δ₃%. Theouter cladding may surround and be in direct contact with the low indexring, the outer cladding comprising a relative refractive index percentΔ₄% relative to pure silica glass, wherein Δ_(1Max)%>Δ₄%≧Δ_(2Max)%.

In yet another embodiment, a bend resistant optical fiber which ismulti-moded at 1300 nm includes a core, an inner cladding, a low indexring and an outer cladding. The core may be formed from silica-basedglass and comprises a graded index of refraction with a core alphaprofile where 1.9≦α_(C)≦2.1, a maximum relative refractive index percentΔ_(1Max)% relative to the outer cladding, and a numerical aperture NA ofgreater than 0.23. The inner cladding may surround and be in directcontact with the core, the inner cladding having a maximum relativerefractive index percent Δ_(2Max)% relative to the outer cladding, aminimum relative refractive index percent Δ_(2Min)% relative to theouter cladding and a radial thickness of at least 0.5 microns, whereinΔ_(2Max)%−Δ_(2Min)%≦0.1% and Δ_(1Max)%>Δ_(2Max)%. The low index ring maysurround and be in direct contact with the inner cladding such that thelow index ring is spaced apart from the core, the low index ring havinga relative refractive index percent Δ₃% relative to the outer cladding,a radial thickness of at least 0.5 microns and a profile volume with anabsolute magnitude of greater than 50%-μm², wherein the minimum relativerefractive index percent Δ_(2Min)% of the inner cladding is greater thanor equal to Δ₃%. The outer cladding may surround and be in directcontact with the low index ring, the outer cladding comprising arelative refractive index percent Δ₄% relative to pure silica glass,wherein Δ_(1Max)%>Δ₄%≧Δ_(2Max)%.

Additional features and advantages of the invention will be set forth inthe detailed description which follows, and in part will be readilyapparent to those skilled in the art from that description or recognizedby practicing the embodiments described herein, including the detaileddescription which follows, the claims, as well as the appended drawings.

It is to be understood that both the foregoing general description andthe following detailed description describe various embodiments and areintended to provide an overview or framework for understanding thenature and character of the claimed subject matter. The accompanyingdrawings are included to provide a further understanding of the variousembodiments, and are incorporated into and constitute a part of thisspecification. The drawings illustrate the various embodiments describedherein, and together with the description serve to explain theprinciples and operations of the claimed subject matter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically depicts a radial cross section of a bend resistantmultimode optical fiber according to one or more embodiments shown anddescribed herein;

FIG. 2 graphically illustrates the relative refractive index percent asa function of radius according to one or more embodiments of a bendresistant optical fiber shown and described herein;

FIG. 3 graphically illustrates the relative refractive index percent asa function of radius according to one or more embodiments of a bendresistant optical fiber shown and described herein; and

FIG. 4 graphically depicts the modeled 1300 nm bandwidth of a bendresistant multimode optical fiber as a function of the spacing betweenthe physical core and the depressed index ring.

DETAILED DESCRIPTION

Reference will now be made in detail to embodiments of bend resistantmultimode optical fibers, examples of which are illustrated in theaccompanying drawings. FIG. 1 schematically depicts a cross section ofan optical fiber according to one or more embodiments shown anddescribed herein. The optical fiber generally comprises a core, an innercladding, a low index ring and an outer cladding. The structure of theoptical fibers as well as the properties of the optical fibers will bedescribed in more detail herein. Whenever possible, the same referencenumerals will be used throughout the drawings to refer to the same orlike parts.

The phrase “refractive index profile,” as used herein, refers to therelationship between refractive index or relative refractive index andoptical fiber radius.

The phrase “relative refractive index percent,” as used herein, isdefined as Δ%=100×(n_(i) ²−n_(REF) ²)/2n_(i) ², where n_(i) is themaximum refractive index in region i, unless otherwise specified. Therelative refractive index percent is measured at 1300 nm unlessotherwise specified. Unless otherwise specified herein, n_(REF) is theaverage refractive index of the outer cladding 140, which can becalculated, for example, by taking “N” index measurements (n_(C1),n_(C2), . . . n_(CN)) in the outer annular region of the cladding (whichin some preferred embodiments may be undoped silica), and calculatingthe average refractive index by:

$n_{C} = {\left( {1/N} \right){\sum\limits_{i = 1}^{i = N}\; n_{Ci}}}$

As used herein, the relative refractive index is represented by Δ andits values are given in units of “%,” unless otherwise specified. Incases where the refractive index of a region is less than the referenceindex n_(REF), the relative index percent is negative and is referred toas having a depressed region or depressed-index, and the minimumrelative refractive index is calculated at the point at which therelative index is most negative unless otherwise specified. In caseswhere the refractive index of a region is greater than the referenceindex n_(REF), the relative index percent is positive and the region canbe said to be raised or to have a positive index.

Macrobend performance is measured according to FOTP-62 (IEC-60793-1-47)by wrapping 1 turn around either a 6 mm, 10 mm, 15 mm, 20 mm, 30 mm orother diameter mandrel as stated (e.g. “1×10 mm diameter macrobend loss”or the “1×15 mm diameter macrobend loss”) and measuring the increase inattenuation due to the bending using an overfilled launch (OFL)condition. The minimum calculated effective modal bandwidths (Min EMBc)may be measured differential mode delay spectra as specified byTIA/EIA-455-220.

Bandwidth may be measured at 1300 nm (unless another wavelength isspecified) according to FOTP-204 with overfilled launch.

As used herein, numerical aperture of the fiber means numerical apertureas measured using the method set forth in TIA SP3-2839-URV2 FOTP-177IEC-60793-1-43 titled “Measurement Methods and Test Procedures-NumericalAperture.”

The term “α-profile” or “alpha profile” refers to a relative refractiveindex profile, expressed in terms of Δ(r) which is in units or “%”,where r is the radius, which follows the equation,Δ(r)=Δ(r ₀)(1[|r−3 ₀|/(r ₁−r₀)]^(α)),where r₀ is the point at which Δ(r) is maximum, r₁ is the point at whichΔ(r)% is zero with respect to pure silica glass, and r is in the ranger_(i)≦r≦r_(f), where Δ is defined above, r_(i) is the initial point ofthe α-profile, r_(f) is the final point of the α-profile, and α is anexponent which is a real number. For a profile segment beginning at thecenterline (r=0), the α-profile has the simpler formΔ(r)=Δ(0)(1−[|r|/(r ₁)]^(α)),where Δ(0) is the refractive index delta at the centerline.

The optical core diameter 2*R_(opt) is measured using the technique setforth in IEC 60793-1-20, titled “Measurement Methods and TestProcedures—Fiber Geometry,” in particular using the reference testmethod outlined in Annex C thereof titled “Method C: Near-field LightDistribution.” To calculate the optical core radius R_(opt) from theresults using this method, a 10-80 fit is applied per section C.4.2.2 toobtain the optical core diameter, which is then divided by 2 to obtainthe optical core radius.

The low index ring has a profile volume, V₃, defined herein as:

2∫_(R_(i))^(R_(o))Δ(r)r 𝕕r

where R_(i) is the innermost radius where Δ₂(r)% is negative withrespect to the outer cladding and R_(o) is the outermost radius of thedepressed-index annular region where Δ₃(r)% is negative with respect toan outer cladding after passing through a minimum. For the fibersdisclosed herein, the absolute magnitude of V₃ is preferably greaterthan 50%-μm², more preferably greater than 140%-μm². In some cases, V₃is greater than 180%-μm² or even greater than 200%-μm².

Referring to FIG. 1, a cross section of an optical fiber 100 multi-modedat 1300 nm is schematically illustrated. The optical fiber generallycomprises a core 110 an inner cladding 120, a low index ring 130, and anouter cladding 140 each of which is formed from silica-based glass. Thecross section of the optical fiber 100 may be generallycircular-symmetric with respect to the center of the core 110.

In the embodiments described herein the core 110 generally comprisessilica glass doped with one or more dopants which increase the index ofrefraction of the glass. In some embodiments, the core comprises silicadoped with germanium (i.e., germania (GeO₂). However, it should beunderstood that dopants other than germanium such as Al₂O₃ or P₂O₅,individually or in combination, may be employed within the core. In someembodiments, the refractive index profile of the optical fiber disclosedherein is non-negative from the centerline to the outer radius of thecore. In some embodiments, the optical fiber contains noindex-decreasing dopants in the core 110. When dopants are present inthe core, the dopants may be distributed throughout the core to obtainthe desired refractive index profile. The core 110 has a relativerefractive index percent Δ₁% relative to the outer cladding and amaximum relative refractive index percent Δ_(1Max)% of greater than 1.6%and less than 2.2%, more preferably greater than 1.6% and less than2.0%, and, most preferably, greater than 1.6% and less than 1.9%. Thenumerical aperture of the core is greater than 0.23, more preferablyfrom about 0.26 to 0.31, and even more preferably from about 0.27 toabout 0.29.

The core 110 has a graded index in a radial direction from the center ofthe core such that the refractive index profile of the core has aparabolic or substantially parabolic shape. In some embodiments therefractive index profile of the core has core alpha profile with an αvalue (α_(C)) between 1.9 and 2.1 as measured at 1300 nm. In someembodiments the refractive index profile of the core may have acenterline dip such that the maximum relative refractive index percentΔ_(1Max)% of the core 110 (and the maximum relative refractive indexpercent of the entire optical fiber) is located a small distance awayfrom the centerline of the optical fiber. However, in other embodiments,the refractive index profile of the core has not centerline dip suchthat the maximum relative refractive index percent Δ_(1Max)% of the core110 (and the maximum relative refractive index percent of the entireoptical fiber) is located at the center of the optical fiber.

The core 110 generally has a physical core radius R₁ and an optical coreradius R_(opt). The physical core radius, as used herein, is the radiusat which the relative refractive index percent Δ₁% of the core firstreaches zero in a radial direction from the center of the core 110. Theoptical core radius R_(opt), as used herein, is half of the optical corediameter. For refractive index profiles of the type shown in FIG. 2,R_(opt) is approximately equal to R₂. For refractive index profiles ofthe type shown in FIG. 3, R₁≦R_(opt)≦R₂ and is modeled by determiningthe radius at which the refractive index equals the effective refractiveindex of the highest mode group with leaky losses of less than 1 dB/m.In the embodiments depicted in FIGS. 2 and 3, R₂ is the innermost radiusat which the relative refractive index of the optical fiber firstreaches a minimum in a radial direction from the center of the core 110.In the embodiments shown and described herein, the core 110 has aphysical core radius R₁ from 26 microns to 33 microns, more preferablyless than 31 microns, even more preferably less than 30.5 microns and,most preferably, less than 30 microns. Further, in the embodimentsdescribed herein the core 110 has an optical core radius R_(opt) from 28microns to 34 microns, more preferably from 29 to 33 microns and, mostpreferably, from 30 to 32.5 microns.

The inner cladding 120 surrounds and is in direct contact with the core110 and extends from the physical core radius R₁ to the radius R₂.Accordingly, it should be understood that the inner cladding has aradial thickness T₂=R₂−R₁. In the embodiments described herein, theradial thickness T₂ of the inner cladding 120 is generally from about0.5 microns to about 5.0 microns.

The inner cladding 120 has a relative refractive index percent Δ₂%relative to the outer cladding 140 and a minimum relative refractiveindex percent Δ_(2Min)% and a maximum relative refractive indexΔ_(2Max)%. The inner cladding 120 may comprise silica glass which issubstantially free from dopants (i.e., the inner cladding 120 is formedfrom pure silica glass). Alternatively, the inner cladding 120 maycomprise one or more dopants which increase or decrease the index ofrefraction of the inner cladding 120. However, the maximum relativerefractive index percent Δ_(2Max)% of the inner cladding 120 willgenerally be less than or equal to the relative refractive index percentΔ₁% of the core and, more specifically, the maximum relative refractiveindex percent Δ_(2Max)% of the inner cladding 120 is less than themaximum relative refractive index percent Δ_(1Max)% of the core 110.

Referring now to FIG. 2, the relative refractive index percent as afunction of the radius of an optical fiber is graphically depicted for abend resistant optical fiber according to one or more embodiments shownand described herein. In the embodiment of the bend resistant opticalfiber depicted in FIG. 2, the relative refractive index percent Δ₂% issubstantially uniform through the radial thickness of the inner cladding120. For example, in one embodiment shown in FIG. 2, the maximumrelative refractive index percent Δ_(2Max)% and the minimum relativerefractive index percent Δ_(2Min)% are the same (i.e.,Δ_(2Max)%=Δ_(2Min)%). In another embodiment, the difference betweenΔ_(2Max)% and Δ_(2Min)% is less than or equal to 0.1% (i.e.,Δ_(2Max)%−Δ_(2Min)%≦0.1%) such that the relative refractive indexpercent Δ₂% is substantially uniform through the radial thickness of theinner cladding. For example, in one embodiment, Δ_(2Max)%≦0.05% whileΔ_(2Min)%≧−0.05% such that the difference between Δ_(2Max)% andΔ_(2Min)% is less than or equal to 0.1%. In embodiments where therelative refractive index percent Δ₂% is substantially uniform throughthe radial thickness of the inner cladding 120, the radial thickness ofthe inner cladding 120 is from about 0.5 microns to about 4.0 microns,more preferably from about 0.75 microns to about 2 microns and, mostpreferably, from about 0.1 micron to about 1.5 microns. Further, inthese embodiments, the physical core radius R₁ is from about 27 micronsto about 33 microns, more preferably from about 28 microns to about 32microns and, most preferably, from about 29 microns to about 31 microns.

While FIG. 2 depicts the relative refractive index Δ₂% of the innercladding 120 as being substantially uniform through the radial thicknessT₂ of the inner cladding 120, it should be understood that in otherembodiments the relative refractive index Δ₂% may vary through theradial thickness of the inner cladding 120.

For example, referring to FIG. 3, a refractive index profile of oneembodiment of a bend resistant multimode optical fiber is graphicallyillustrated where the relative refractive index percent Δ₂% variesthrough the radial thickness of the inner cladding 120. In oneembodiment, the index of refraction of the inner cladding decreasesbetween R₁ and R₂ such that the relative refractive index percent Δ₂% isgraded in a radial direction, as depicted in FIG. 3. For example, therefractive index profile of the inner cladding may have an innercladding alpha profile with an α value (α_(IC)). In some embodiments,the refractive index profile of the inner cladding 120 may be anextension of the refractive index profile of the core 110. For example,the inner cladding may have an α value α_(IC) from about 1.9 to about2.1 such that the inner cladding is a continuation of the graded indexprofile of the core. In this embodiment the graded index of therefraction of the core continues past R₁ and into the inner cladding 120where the relative refractive index percent Δ₂% is negative between R₁and R₂.

In another embodiment, the α-shape of the inner cladding 120 is afunction of the α-shape of the core 110. For example, in thisembodiment, the inner cladding may have an α value α_(IC) from 0.8*α_(C)to 1.2*α_(C). In this embodiment the graded index of refraction of thecore also continues past R₁ and into the inner cladding 120 where therelative refractive index percent Δ₂% is negative between R₁ and R₂.However, in this embodiment the α-shape of the inner cladding may beslightly different than the α-shape of the core. In either embodimentthe inner cladding 120 has a maximum relative refractive index percentΔ_(2Max)% at R₁, which decreases over the radial thickness of the innercladding to a minimum relative refractive index percent Δ_(2Min)% at R₂.Accordingly, it should be understood that Δ₁%≧Δ_(2Max)% andΔ_(1Max)%>Δ_(2Max)%. In these embodiments Δ_(2Max)%<−0.05%.

Further, where the relative refractive index percent Δ₂% varies throughthe radial thickness of the inner cladding 120, the inner cladding 120has radial thickness T₂ from about 1 micron to about 5 microns, morepreferably greater than about 1.5 microns and, most preferably, greaterthan about 2.0 microns. Further, in these embodiments, the physical coreradius is from about 26 microns to about 31 microns, more preferablyfrom about 27 microns to about 30 microns.

Referring now to FIGS. 1-3, the low index ring 130 surrounds and is indirect contact with the inner cladding 120 such that the low index ring130 is spaced apart from the core 110. The low index ring extends fromthe optical radius R₂ to a radius R₃ such that the low index ring has aradial thickness T₃=R₃−R₂. The radius R₃, as used herein, refers to theradius of the optical fiber 100 at which the relative refractive indexof the optical fiber 100 reaches a value of 0.05% after passing througha minimum in the radial direction from the centerline of the opticalfiber. In the embodiments described herein the radial thickness T₃ ofthe low index ring 130 may be from about 2.0 microns to about 8.0microns, more preferably from about 4 microns to about 6 microns. Thelow index ring 130 may be formed from silica glass which includes one ormore dopants which decrease the index of refraction of the silica glass.For example, the low index ring 130 may include silica glass doped withfluorine, boron or various combinations thereof. However, it should beunderstood that other dopants may be used to decrease the index ofrefraction of the low index ring 130.

The low index ring 130 generally has a relative refractive index percentΔ₃% with respect to the outer cladding with a minimum relativerefractive index percent Δ_(3Min)% and a maximum relative refractiveindex percent Δ_(3Max)%. The relative refractive index Δ₃% of the lowindex ring 130 is less than zero through the radial thickness of the lowindex ring. In one embodiment, the relative refractive index percent Δ₃%is substantially uniform through the radial thickness of the low indexring 130 (i.e., from R₂ to R₃) such that Δ_(3Min)%=Δ_(3Max)%. However,it should be understood that, in other embodiments, Δ₃% may vary betweenR₂ and R₃. In general, the relative refractive index Δ₃% of the lowindex ring 130 is less than or equal to Δ_(2Min)%. As describedhereinabove, the low index ring 130 may have a profile volume V₃ with anabsolute magnitude preferably greater than 50%-μm², more preferablygreater than 100%-μm² and even more preferably greater than 140%-μm².

An outer cladding 140 is disposed around the low index ring 130 suchthat the outer cladding 140 surrounds and is in direct contact with thelow index ring 130. The outer cladding 140 extends from R₃ to R₄. In theembodiments described herein, R₄ may be from about 40 microns to about62.5 microns. The outer cladding 140 may generally have a radialthickness T₄=R₄−R₃. In the embodiments described herein, T₄ may be fromabout 10 microns to about 30 microns, more preferably less than about 25microns. In some embodiments the outer cladding 140 is formed from puresilica glass. The term pure silica glass, as used herein, means that thesilica glass does not contain dopants in concentrations which wouldsignificantly modify (i.e., increase or decrease) the index ofrefraction of pure silica glass. In these embodiments, the relativeindex of refraction Δ₄% of the outer cladding 140 is zero relative topure silica glass. In other embodiments, the outer cladding 140 has amaximum relative index of refraction percent Δ_(4Max)% which is lessthan 0.05% and a minimum relative index of refraction percent Δ_(4Min)%which is greater than −0.05%. In this embodiment, the low index ring 130ends where Δ₃% reaches a value of greater than −0.05% going radiallyoutward after passing through Δ_(3Min)%. In general, the outer cladding140 has a relative refractive index Δ₄% such thatΔ_(1Max)%>Δ₄%≧Δ_(2Max)%.

Accordingly, the glass portion of the optical fiber 100 (e.g., the core102, the inner cladding 104, the low index ring 106, and the outercladding 108) may have a diameter of 2R₄. In the embodiments describedherein, the diameter of the glass portion of the optical fiber isbetween 120 and 130 μm, preferably about 125 μm.

The optical fiber 100 shown in FIG. 1 may be formed by conventionalfiber manufacturing techniques. For example, the various layers (e.g.,the inner cladding 120, the low index ring 130, and the outer cladding140) may be formed on a core cane member to create a fiber preform usingvarious vapor phase deposition techniques such as chemical vapordeposition (CVD), modified chemical vapor deposition (MCVD), or anyother vapor phase deposition technique used in the manufacture ofoptical fiber preforms. Alternatively, the fiber preform may be formedusing rod-in-tube techniques where a core cane member is “sleeved” witha glass tube or tubes having the desired characteristics. The resultingfiber preform formed from the aforementioned processes may thereafter bedrawn into optical fiber.

After the optical fiber 100 is drawn from the fiber preform, the opticalfiber 100 may be coated with one or more coatings (not shown). Forexample, in one embodiment, optical fiber 100 may be coated with a lowmodulus primary coating and a high modulus secondary coating.

Optical fibers according to the embodiments described herein have largenumerical apertures (e.g., NA≧0.23) and overfilled launch (OFL)bandwidths at 1300 nm of greater than 1000 MHz-km, more preferablygreater than 1500 MHz-km and, more preferably, greater than 2000 MHz-km.In some embodiments, the OFL bandwidth at 1300 nm of the optical fibersdescribed herein is greater than 3000 MHz-km, more preferably greaterthan 4000 MHz-km and, most preferably, greater than 5000 MHz-km. Inaddition, optical fibers according to the embodiments described hereinhave improved bending performance. For example, the optical fibersexhibit a 1×10 mm diameter macrobend loss of less than 0.2 dB at awavelength of 1300 nm, more preferably less than 0.1 dB and, mostpreferably, less than 0.05 dB.

EXAMPLES

The various embodiments of optical fibers will be further clarified bythe following modeled examples of various embodiments of the highnumerical aperture, bend resistant optical fibers set forth in Tables1-4 below. Specifically, Tables 1-4 list various modeled values forΔ_(1Max)%, R₁, α_(C), Δ_(2Max)%, R₂, Δ_(3Max)%, R₃, V₃, the OFLbandwidth of the optical fiber at 1300 nm, and the 1×10 mm diametermacrobend loss for 20 modeled optical fibers.

Examples 1-6

The optical fiber examples contained in Table 1 have physical core radiifixed at 31.25 microns while the maximum relative refractive indexΔ_(1Max)% of the core ranges from about 1.9% to about 2.0%. Theembodiments of the optical fibers shown in Table 1 have numericalapertures of 0.29 and optical core diameters of greater than 62.5microns.

Referring to FIG. 4, the modeled overfill launch (OFL) bandwidth at 1300nm for an optical fiber according to one or more embodiments shown anddescribed herein, is graphically depicted as a function of the radius R₂of the inner cladding. The various data points comprising the curverepresent optical fibers with a fixed optical core radius R₁ of 31.25microns (i.e., optical fibers such as those described in Table 1). Asshown in FIG. 4, high OFL bandwidths may be achieved when the radialthickness T₂ of the inner cladding is greater than about 0.5 microns andless than about 4 microns, more preferably greater than about 1 micronand less than 2 microns, and most preferably, greater than about 1micron and less than about 1.5 microns. FIG. 4 also graphicallydemonstrates that a peak OFL bandwidth of greater than 3500 MHz-km maybe achieved utilizing the fiber designs described herein.

TABLE 1 Example1 Example2 Example3 Example4 Example5 Example6 Δ_(1Max) %1.974 1.974 1.956 1.977 1.963 1.963 R₁ (μm) 31.25 31.25 31.25 31.2531.25 31.25 α_(c) 2.000 2.000 1.999 1.987 1.991 1.991 Δ_(2Max) % 0 0 0 00 0 R₂ (μm) 32.48 32.58 32.70 32.67 32.35 32.24 R_(opt) (μm) 32.48 32.5832.70 32.67 32.35 32.24 Δ_(3Min) % −0.45 −0.45 −0.45 −0.55 −0.36 −0.36R₃ (μm) 37.75 37.75 39.03 37.00 39.63 39.63 V₃ (%-sq. μm) −166.5 −163.6−202.6 −166.0 −190.0 −192.6 R₄ (μm) 62.5 62.5 62.5 62.5 62.5 62.5 BW13002157 2789 1777 3096 3864 2077 (MHz-km) Optical Core 65.0 65.2 65.4 65.364.7 64.5 Diameter (μm) 1 × 10 mm 0.04 0.04 0.02 0.04 0.03 0.03 BendLoss (dB/turn)

Examples 7-10

The optical fiber examples contained in Table 2 have a physical coreradius fixed at 31.25 microns, as with the optical fiber examples inTable 1. However, the maximum relative refractive index Δ_(1Max)% of thecore in optical fiber Examples 7-10 is less than 1.9%. Maintaining themaximum relative refractive index Δ_(1Max)% below 1.9% reduces thenumerical aperture NA of the optical fiber to approximately 0.28 whichimproves the compatibility of the optical fiber with existing 62.5micron optical core diameter fiber. However, the fiber designs shown inTable 2 have improved OFL bandwidth at 1300 nm compared to existing 62.5micron fibers in addition to low bend losses.

TABLE 2 Example 7 Example 8 Example 9 Example 10 Δ_(1Max)% 1.829 1.7601.796 1.855 R₁ (μm) 31.25 31.25 31.25 31.25 α_(c) 1.992 1.998 1.9961.997 Δ_(2Max)% 0 0 0 0 R₂ (μm) 32.63 32.73 32.66 32.68 R_(opt) (μm)32.63 32.73 32.66 32.68 Δ_(3Min)% −0.48 -0.48 -0.48 -0.48 R₃ (μm) 37.4438.96 38.18 38.85 V₃ (%-sq.μm) −162 −216 −188 −212 R₄ (μm) 62.5 62.562.5 62.5 BW1300 (MHz-km) 4311 4237 4090 4056 Optical Core 65.3 65.565.3 65.4 Diameter (μm) 1 × 10 mm Bend 0.04 0.02 0.03 0.02 Loss(dB/turn)

Examples 11-16

The optical fiber examples contained in Table 3 have optical corediameters of 62.5 microns and numerical apertures NA of 0.28 which arecompatible with existing 62.5 micron fiber designs. However, the fiberdesigns shown in Table 3 have improved OFL bandwidth at 1300 nm comparedto existing 62.5 micron fibers in addition to low bend losses. Examples15 and 16 are optical fiber designs with outer cladding diameters of 90microns and 80 microns respectively.

TABLE 3 Example11 Example12 Example13 Example14 Example15 Example16Δ_(1Max) % 1.813 1.788 1.714 1.683 1.680 1.684 R₁ (μm) 29.88 29.82 29.8429.81 29.71 29.70 α_(c) 1.994 1.997 1.999 2.000 1.999 2.003 Δ_(2Max) % 00 0 0 0 0 R₂ (μm) 31.25 31.25 31.25 31.25 31.25 31.25 R₂ (μm) 31.2531.25 31.25 31.25 31.25 31.25 Δ_(3Min) % −0.48 −0.48 −0.45 −0.45 −0.52−0.52 R₃ (μm) 37.50 38.15 38.01 37.95 37.29 36.11 V₃ (%-sq. μm) −206−230 −212 −207 −217 −170 R₄ (μm) 62.5 62.5 62.5 62.5 45 40 BW1300 45994189 4286 3916 4783 3696 (MHz-km) Optical Core 62.5 62.5 62.5 62.5 62.562.5 Diameter (μm) 1 × 10 mm 0.02 0.02 0.02 0.02 0.02 0.04 Bend Loss(dB/turn)

Examples 17-20

The optical fiber examples contained in Table 4 have an inner claddingwhich has a graded index of refraction extending between the physicalcore radius R₁ and an outer core radius R₂. The optical fibers in theseexamples have R1≦Ropt≦R2, an optical core diameter of 62.5 microns withnumerical apertures of at least 0.23, high OFL bandwidths at 1300 nm andlow bend losses.

TABLE 4 Example 17 Example 18 Example 19 Example 20 Δ_(1Max) (%) 1.6761.668 1.691 1.706 R₁ (μm) 28.01 28.19 27.88 29.38 α_(c) 1.996 1.9961.995 1.994 R₂ (μm) 31.53 32.16 31.58 32.77 Δ_(3Min) (%) -0.436 -0.491-0.461 -0.404 R₃ (μm) 37.74 37.98 38.01 37.89 V₃ (%-sq.μm) -231 -256-257 -186 R₄ (μm) 62.5 62.5 62.5 62.5 BW1300 5188 5152 5105 5089(MHz-km) Optical Core 62.5 62.5 62.5 62.5 Diameter (μm) 1 × 10 mm 0.020.01 0.01 0.03 Bend Loss (dB/turn)

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the embodiments describedherein without departing from the spirit and scope of the claimedsubject matter. Thus it is intended that the specification cover themodifications and variations of the various embodiments described hereinprovided such modification and variations come within the scope of theappended claims and their equivalents.

1. A bend resistant optical fiber which is multi-moded at 1300 nmcomprising a core, an inner cladding, a low index ring and an outercladding, wherein: the core is formed from silica-based glass andcomprises a graded index of refraction with a core alpha profile where1.9≦α_(C)≦2.1, a maximum relative refractive index percent Δ_(1Max)%relative to the outer cladding, and a numerical aperture NA of greaterthan 0.23; the inner cladding surrounds and is in direct contact withthe core, the inner cladding having a maximum relative refractive indexpercent Δ_(2Max)% relative to the outer cladding, a minimum relativerefractive index percent Δ_(2Min)% relative to the outer cladding, and aradial thickness of at least 0.5 microns, wherein Δ_(1Max)% is greaterthan Δ_(2Max)%; the low index ring that surrounds and is in directcontact with the inner cladding such that the low index ring is spacedapart from the core, the low index ring having a relative refractiveindex percent Δ₃% relative to the outer cladding, a radial thickness ofat least 0.5 microns and a profile volume with an absolute magnitude ofgreater than 50%-μm², wherein the minimum relative refractive indexpercent Δ_(2Min)% of the inner cladding is greater than or equal to Δ₃%;and the outer cladding surrounds and is in direct contact with the lowindex ring, the outer cladding comprising a relative refractive indexpercent Δ₄% relative to pure silica glass, whereinΔ_(1Max)%>Δ₄%≧Δ_(2Max)%.
 2. The optical fiber of claim 1 wherein arelative refractive index percent Δ₂% of the inner cladding issubstantially uniform through the radial thickness of the inner claddingsuch that Δ_(2Max)%−Δ_(2Min)%≦0.1%.
 3. The optical fiber of claim 2wherein Δ_(2Max)%≦0.05% and Δ_(2Min)%≧−0.05%.
 4. The optical fiber ofclaim 2 wherein the radial thickness of the inner cladding is less thanor equal to 4 microns.
 5. The optical fiber of claim 2 wherein aphysical radius of the core is greater than or equal to 27 microns andless than or equal to 33 microns.
 6. The optical fiber of claim 1wherein the inner cladding comprises a graded index of refraction withan inner cladding alpha profile where 0.8*α_(C)≦α_(IC)≦1.2*α_(C).
 7. Theoptical fiber of claim 6 wherein the minimum relative refractive indexΔ_(2Min)% of the inner cladding is less than −0.05%.
 8. The opticalfiber of claim 6 wherein the radial thickness of the inner cladding isgreater than 1 micron.
 9. The optical fiber of claim 6 wherein aphysical radius of the core is greater than or equal to 26 microns andless than or equal to 31 microns.
 10. The optical fiber of claim 1wherein 0.26≦NA≦0.30.
 11. The optical fiber of claim 1 wherein1.6%≦Δ_(1Max)%≦2.0%.
 12. The optical fiber of claim 1 wherein theoptical fiber exhibits a 1 turn 10 mm diameter mandrel wrap attenuationincrease of less than or equal to 0.2 dB at 1300 nm.
 13. The opticalfiber of claim 1 wherein an optical radius of the core is greater thanor equal to 28 microns and less than or equal to 34 microns.
 14. Theoptical fiber of claim 1 wherein the fiber exhibits an overfilledbandwidth greater than 1000 MHz-km at 1300 nm.
 15. A bend-resistantoptical fiber which is multi-moded at 1300 nm comprising a core, aninner cladding, a low index ring, and an outer cladding, wherein: thecore is formed from silica-based glass and comprises a graded index ofrefraction with a core alpha profile where 1.9≦α_(C)≦2.1, a maximumrelative refractive index percent Δ_(1Max)% relative to pure silicaglass, and a numerical aperture NA of greater than 0.23; the innercladding surrounds and is in direct contact with the core, the innercladding having a graded index of refraction with an inner claddingalpha profile α_(IC), a maximum relative refractive index percentΔ_(2Max)% relative to pure silica glass, and a minimum relativerefractive index percent Δ_(2Min)% relative to pure silica glass,wherein Δ_(1Max)%>Δ_(2Max)%; the low index ring surrounds and is indirect contact with the extended core region such that the low indexring is spaced apart from the core, the low index ring having a relativerefractive index percent Δ₃% relative to pure silica glass, a radialthickness of at least 1 micron and a profile volume with an absolutemagnitude of greater than 50%-μm², wherein Δ_(2Min)%≧Δ₃%; the outercladding surrounds and is in direct contact with the low index ring, theouter cladding comprising a relative refractive index percent Δ₄%relative to pure silica glass, wherein Δ_(1Max)%>Δ₄%≧Δ_(2Max)%.
 16. Theoptical fiber of claim 15 wherein a physical radius of the core isgreater than or equal to 26 microns and less than or equal to 31microns.
 17. The optical fiber of claim 16 wherein0.8*α_(C)≦α_(IC)≦1.2*α_(C).
 18. A bend resistant optical fiber which ismulti-moded at 1300 nm comprising a core, an inner cladding, a low indexring and an outer cladding, wherein: the core is formed fromsilica-based glass and comprises a graded index of refraction with acore alpha profile where 1.9≦α_(C)≦2.1, a maximum relative refractiveindex percent Δ_(1Max)% relative to pure silica glass, and a numericalaperture NA of greater than 0.23; the inner cladding surrounds and is indirect contact with the core, the inner cladding having a maximumrelative refractive index percent Δ_(2Max)% relative to pure silicaglass, a minimum relative refractive index percent Δ_(2Min)% relative topure silica glass, a radial thickness of at least 0.5 microns, whereinΔ_(2Max)%−Δ_(2Min)≦0.1% and Δ_(1Max)%>Δ_(2Max)%; the low index ring thatsurrounds and is in direct contact with the inner cladding such that thelow index ring is spaced apart from the core, the low index ring havinga relative refractive index percent Δ₃% relative to pure silica glass, aradial thickness of at least 0.5 microns and a profile volume with anabsolute magnitude of greater than 50%-μm², wherein the minimum relativerefractive index percent Δ_(2Min)% of the inner cladding is greater thanor equal to Δ₃%; and the outer cladding surrounds and is in directcontact with the low index ring, the outer cladding comprising arelative refractive index percent Δ₄% relative to pure silica glass,wherein Δ_(1Max)%>Δ₄%≧Δ_(2Max)%.
 19. The optical fiber of claim 18wherein Δ_(2Max)%≦0.05% and Δ_(2Min)%≦−0.05%.
 20. The optical fiber ofclaim 18 wherein the radial thickness of the inner cladding is less thanor equal to 4 microns.